Photoresist compositions are used in microlithographic processes for making miniaturized electronic components, such as in the fabrication of semiconductor device structures. The miniaturized electronic device structure patterns are typically created by transferring a pattern from a patterned masking layer overlying the semiconductor substrate, rather than by direct write on the semiconductor substrate, because of the time economy which can be achieved by blanket processing through a patterned masking layer. With regard to semiconductor device processing, the patterned masking layer may be a patterned photoresist layer or may be a patterned “hard” masking layer (typically an inorganic material or a high temperature organic material) which resides on the surface of the semiconductor device structure to be patterned. The patterned masking layer is typically created using another mask which is frequently referred to as a photomask or reticle. A reticle is typically a thin layer of a metal-containing layer (such as a chrome-containing, molybdenum-containing, or tungsten-containing material, for example) deposited on a glass or quartz plate. The reticle is patterned to contain a “hard copy” of the individual device structure pattern to be recreated on the masking layer overlying a semiconductor structure.
A reticle may be created by a number of different techniques, depending on the method of writing the pattern on the reticle. Due to the dimensional requirements of today's semiconductor structures, the writing method is generally with a laser or e-beam. A typical process for forming a reticle may include: providing a glass or quartz plate, depositing a chrome-containing layer on the glass or quartz surface, depositing an antireflective coating (ARC) over the chrome-containing layer, applying a photoresist layer over the ARC layer, direct writing on the photoresist layer to form a desired pattern, developing the pattern in the photoresist layer, etching the pattern into the chrome layer, and removing the residual photoresist layer. When the area of the photoresist layer contacted by the writing radiation becomes easier to remove during development, the photoresist is referred to as a positive-working photoresist. When the area of the photoresist layer contacted by the writing radiation becomes more difficult to remove during development, the photoresist is referred to as a negative-working photoresist. Advanced reticle manufacturing materials frequently include combinations of layers of materials selected from chromium, chromium oxide, chromium oxynitride, molybdenum, molybdenum silicide, and molybdenum tungsten silicide, for example.
As previously mentioned, the reticle or photomask is used to transfer a pattern to an underlying photoresist, where the reticle is exposed to blanket radiation which passes through open areas of the reticle onto the surface of the photoresist. The photoresist is then developed and used to transfer the pattern to an underlying semiconductor structure. Due to present day pattern dimensional requirements, which are commonly less than 0.3 μm, the photoresist is preferably a chemically amplified DUV photoresist. In the making of the reticle itself, a chemically amplified DUV photoresist has been used in combination with a direct write electron beam writing tool. Additional work has been done recently using a direct write continuous wave laser tool available under the trade name ALTA™ from ETEC Systems Inc., Hillsboro, Oreg.
Preparation of a photomask/reticle is a complicated process involving a number of interrelated steps which affect the critical dimensions of a pattern produced in the reticle, and the uniformity of the pattern critical dimensions across the surface area of the reticle. By changing various steps in the reticle manufacturing process, the reproducibility of the manufacturing process itself may be altered, including the processing window. Processing window refers to the amount process conditions can be varied without having a detrimental outcome on the product produced. The larger the processing window, the greater change permitted in processing conditions without a detrimental affect on the product. Thus, a larger process window is desirable, as this generally results in a higher yield of in specification product produced.
The reticle manufacturing process steps generally include the following, where the initial substrate used to form the reticle is a silicon oxide-containing base layer having a layer of a metal-containing (typically chrome) mask material applied thereover. An inorganic antireflective coating (ARC) or an organic ARC, or a combination of inorganic and organic ARC layers may be applied over the surface of the chrome mask material. A photoresist layer is then applied over the antireflective coating. The photoresist is typically an organic material which is dissolved or dispersed in a solvent. The solution or dispersion of photoresist is typically spin coated onto the surface of the photomask fabrication structure. Typically, the photoresist is applied over an ARC layer on the fabrication structure surface. Some of the solvent or dispersion medium is removed during the spin coating operation. Residual solvent or dispersion medium is subsequently removed by another means, typically by baking the fabrication structure, including the photoresist layer. This step is commonly referred to as “Post Apply Bake” or PAB. The photoresist is then exposed to radiation (imaged), to produce a pattern in the photoresist layer, typically by a direct write process when the pattern includes dimensions which are less than about 0.3 μm. After exposure, the substrate including the photoresist layer is baked again. The second baking is typically referred to as “Post Exposure Bake” or PEB. The photoresist is then developed either using a dry process or a wet process, to create the pattern having openings through the photoresist layer thickness. Once the photoresist is “patterned” so that the pattern openings extend through the photoresist layer to the upper surface of an ARC layer, or to a surface beneath an ARC layer, the pattern in the patterned photoresist is transferred through the chrome-based mask layer and any remaining layers overlying the chrome layer, for example, typically by dry etching.
U.S. Pat. No. 6,303,169, issued Mar. 9, 2004 to Fuller et al., titled: “Method Of Preparing Optically Imaged High Performance Photomasks”, and assigned to the assignee of the present invention, describes a method of producing a reticle via an optically imaged photoresist using a direct write continuous wave laser. In particular, the invention pertains to a method of optically fabricating a photomask using a direct write continuous wave laser, which includes the steps of applying an organic antireflection coating over a metal-containing layer; applying a chemically-amplified DUV photoresist, either positive tone or negative tone, over the organic antireflection coating; baking the DUV photoresist at a temperature within a specifically designed range under ambient conditions, with volatile removal assisted by an exhaust hood fan or by similar method (PAB); exposing a surface of the DUV photoresist to radiation from the direct write continuous wave laser; baking the developed photoresist at a temperature within a specifically designed range, again under ambient conditions using an exhausted hot plate (PEB); and, developing the image within the DUV photoresist. Preferably the laser used to image the DUV photoresist is operated at 244 or 257 nm, although other wavelengths may be used. Subsequently, the developed, patterned photoresist is used as a mask for transferring the pattern through a metal-containing layer of the photomask substrate. Typically the pattern transfer is by dry etch. The metal-containing layer of the photomask substrate may include combinations of layers of materials selected from chromium, chromium oxide, chromium oxynitride, molybdenum, molybdenum silicide, and molybdenum tungsten silicide, for example and not by way of limitation. This patent is hereby incorporated by reference in its entirety.
U.S. Pat. No. 6,605,394, issued Aug. 12, 2003 to Montgomery et al., titled: “Organic Bottom Antireflective Coating For High Performance Mask Making Using Optical Imaging”, and assigned to the assignee of the present invention, also describes a reticle fabrication process, with emphasis on the bottom ARC layers used beneath the photoresist, during patterning of the photoresist. One embodiment of the invention pertains to a method of optically fabricating a photomask using a direct write continuous wave laser, which includes the steps of applying an organic antireflection coating over a metal-containing layer; applying a chemically-amplified DUV photoresist, either positive tone or negative tone, over the organic antireflection coating; and exposing a surface of the DUV photoresist to radiation from the direct write continuous wave laser. Preferably the laser is operated at 244 nm or 257 nm. The metal-containing layer may include combinations of layers of materials selected from chromium, chromium oxide, chromium oxynitride, molybdenum, molybdenum silicide, and molybdenum tungsten silicide, for example and not by way of limitation. The organic antireflection coating may be selected from a negative photoresist containing a DUV dye; a polymeric material prepared from acrylic polymers or copolymers; a binder resin combined with an acid or thermal acid generator and a photoacid generator compound; a binder resin having pendent phenyl groups; and combinations thereof. The organic anti-reflective coating composition preferably comprises acrylic polymers and/or copolymers. In an alternative embodiment of the method of fabricating a photomask, the organic antireflection-coating is applied over an inorganic antireflection coating. The inorganic antireflection coating may be selected to include a material such as chrome oxynitride, titanium nitride, silicon nitride or molybdenum silicide. The '394 patent describes a reticle fabrication process which employs a new direct pattern writing tool which is a 244 nm or a 257 nm mask writing laser available from ETEC Systems Inc., Hillsboro, Oreg. This patent is hereby incorporated by reference in its entirety. Additional information about process variables in the 257 nm direct writing of photomask patterns is provided in U.S. Pat. No. 6,703,169, referenced above.
As disclosed in the '394 patent, there are a number of problems encountered in trying to produce a photomask/reticle when the photomask pattern exhibits critical dimensions of less than 0.3 μm. Further, producing a reticle where pattern critical dimensions are uniform across the entire reticle surface requires careful control of process variables in each step of the reticle manufacturing process.
U.S. Pat. No. 6,727,047 issued Apr. 27, 2004 to Montgomery et al., titled: “Method Of Extending The Stability Of A Photoresist During Direct Writing Of An Image Upon The Photoresists”, and assigned to the assignee of the present invention, describes a method of reducing the environmental sensitivity of a chemically amplified photoresist This improves the process window during imaging and development of the chemically amplified photoresist. The photoresist is overcoated with a thin coating (topcoat) of a protective but transmissive material. It is particularly helpful if the topcoat material exhibits a refractive index and thickness which is matched to the refractive index and thickness of the photoresist. In addition, to provide improved stability when the time period required for direct writing of a pattern on the photoresist is a long time, in excess of about 2 hours, for example, the topcoat is pH adjusted to be as neutral in pH as possible, depending on other process variable requirements. By application of a pH adjusted protective topcoat, described above, over a chemically amplified photoresist, it is possible to prepare an unexposed photoresist-coated substrate (wafer or reticle) months before its actual exposure to radiation, and to maintain the substrate in a patterning (radiation imaging) tool for longer time periods. U.S. Pat. No. 6,727,047 is hereby incorporated by reference in its entirety.
The disadvantage of using a topcoat is that the topcoat may gradually disperse into the underlying chemically amplified photoresist and affect the performance of the chemically amplified photoresist, depending on the composition of the particular photoresist.
The chemically amplified photoresist used during development of the experimental data provided in U.S. Pat. Nos. 6,703,169; 6,605,394; and 6,727,047 was generally for a chemically amplified DUV photoresist, DX1100 supplied by AZ-Clariant Corp. of Somerville, N.J. This photoresist comprises a modified phenolic polymer; propylene glycol monomethyl ether acetate (PGMEA); 1-methoxy-2-propyl acetate; and, an onium salt metal halide complex as a chemical amplifier.
During more recent development of the reticle manufacturing process, we worked to reduce the minimum feature size which could be imaged (printed) using the optical imaging direct write continuous wave laser described above. In addition, we made a major effort to improve the uniformity of the critical dimension of a feature size across the entire reticle surface.
The present invention pertains to improving the reticle processing window in a manner which enables patterning of smaller dimension features and which enables better uniformity of features across the reticle. In particular, the invention relates to an improvement in photoresist behavior during the pattern irradiation (frequently referred to as imaging or printing) of a chemically amplified positive photoresist and during pattern development of the positive photoresist.